Airworthiness Directives; The Boeing Company Airplanes

SUPPLEMENTARY INFORMATION:

Comments Invited

The FAA invites you to send any written relevant data, views, or arguments about this proposal. Send your comments to an address listed under the ADDRESSES section. Include “Docket No. FAA-2023-2151; Project Identifier AD-2023-00984-T” at the beginning of your comments. The most helpful comments reference a specific portion of the proposal, explain the reason for any recommended change, and include supporting data. The FAA will consider all comments received by the closing date and may again revise this proposal because of those comments.

Except for Confidential Business Information (CBI) as described in the following paragraph, and other information as described in 14 CFR 11.35, the FAA will post all comments received, without change, to regulations.gov, including any personal information you provide. The agency will also post a report summarizing each substantive verbal contact received about this proposed AD.

Confidential Business Information

CBI is commercial or financial information that is both customarily and actually treated as private by its owner. Under the Freedom of Information Act (FOIA) (5 U.S.C. 552), CBI is exempt from public disclosure. If your comments responsive to this SNPRM contain commercial or financial information that is customarily treated as private, that you actually treat as private, and that is relevant or responsive to this SNPRM, it is important that you clearly designate the submitted comments as CBI. Please mark each page of your submission containing CBI as “PROPIN.” The FAA will treat such marked submissions as confidential under the FOIA, and they will not be placed in the public docket of this SNPRM. Submissions containing CBI should be sent to Luis Cortez-Muniz, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 206-231-3958; email: Luis.A.Cortez-Muniz@faa.gov. Any commentary that the FAA receives that is not specifically designated as CBI will be placed in the public docket for this rulemaking.

Background

The FAA issued an NPRM to amend 14 CFR part 39 by adding an AD that would apply to all The Boeing Company Model 777-200, -200LR, -300, -300ER, and 777F series airplanes. The NPRM published in the Federal Register on November 17, 2023 (88 FR 80216). The NPRM was prompted by a report of a 5-inch crack on the right wing upper wing skin at wing station (WSTA) 460. In the NPRM, the FAA proposed to require repetitive inspections for cracking of the upper wing skin common to certain fasteners and applicable on-condition actions, including repair.

Actions Since the NPRM Was Issued

Since the FAA issued the NPRM, Boeing advised the FAA that there have been two events of cracking at the fastener 6 and 7 locations where the cracks initiated in the spanwise (inboard/outboard) direction. These events were detected only because of a repair for an adjacent fastener; the repaired fastener 6 and 7 locations were subsequently inspected with an open hole HFEC inspection, and not with the UT inspection. UT inspections can only detect cracking growth in a particular direction if certain inspection procedures are performed. The Model 777 non-destructive testing (NDT) procedures, which are specified in Boeing Alert Requirements Bulletin 777-57A0125 RB, dated July 25, 2023, include inspections for cracks initiating in the chordwise (forward/aft) direction, which was how cracking was expected to initiate based on Boeing analysis. A UT inspection at the fastener 6 and 7 locations would not have adequately detected the cracks found by the open hole HFEC inspection. As a result, the existing inspections will not provide a sufficient assessment of the structure before a crack reaches critical length. An open hole HFEC inspection, however, can detect cracking initiating from any direction.

Comments

The FAA received comments from two individuals who supported the NPRM without change.

The FAA received additional comments from seven commenters, including Air France, American Airlines, Air New Zealand, Boeing, Etihad Airways, FedEx Express (FedEx), and United Airlines (United). The following presents the comments received on the NPRM and the FAA's response to each comment.

Request for Defined Repairs

Air France requested that a predefined preventive repair that includes required parts and instructions be developed, approved by the FAA, and provided as optional terminating action for the repetitive inspections.

Air France also requested that a permanent repair be developed. The commenter is concerned with the difficulty of anticipating the repair process and unscheduled aircraft ground time.

The FAA does not concur with this request because the agency has not yet received a permanent repair procedure from Boeing. However, the FAA will review and consider approval of repair procedures and issue an alternative method of compliance (AMOC) if they are acceptable.

Requests for Extension of Repeat Inspection Interval

Air France requested that the repeat inspection interval for Groups 4 and 6 be increased based on the results of the initial inspections and on the age of the airplane. Air France added that the intervals are shorter than the interval of appropriate maintenance checks for some operators.

FedEx requested that less-frequent inspections be permitted because Boeing Alert Requirements Bulletin 777-57A0125 RB, dated July 25, 2023, does not account for the average mission length, which FedEx asserted is a dominant factor. FedEx stated that Boeing analysis indicated that crack initiation on high gross weight airplanes with an average mission length of six flight hours per flight cycle is not expected to occur until a significantly higher number of flight cycles than on an airplane with an average mission length of eight flight hours per flight cycle. FedEx stated that excessively conservative inspection intervals will increase the probability of unnecessary removal of fasteners due to false indications, creating an added risk of incidental damage. FedEx proposed revised compliance times for airplanes with an average mission length of six flight hours per flight cycle.

The FAA does not concur with the request to extend the repeat inspection interval required by this proposed AD. The FAA notes that the commenters did not provide sufficient supporting data and analysis to show that revised inspection intervals would provide an adequate level of safety. Further, the analysis FedEx mentioned was an informal analysis from 2023 before most operators began performing the required inspections. Since that analysis, there have been numerous additional findings, including some on airplanes with an average mission length of less than six flight hours per flight cycle. However, the FAA may consider changes in the compliance time provided that sufficient data is submitted in the future and in accordance with paragraph (i) of this proposed AD.

Request for Corrections to NDT Manual Sections

American Airlines requested corrections to several discrepancies in the 777 NDT Manual Part 4, sections 57-20-13 and 57-20-14, which provide ultrasonic inspection procedures. For section 57-20-13, American Airlines coordinated with Boeing to correct issues in the NDT procedure. American Airlines added that in Section 57-20-14, the figure was oriented incorrectly. American Airlines provided images of how the figure should be illustrated.

The FAA agrees with the corrections requested by American Airlines. The FAA contacted Boeing to review changes planned in a later revision of 777 NDT Manual Part 4, sections 57-20-13 and 57-20-14. These revisions have since been released as 777 NDT Manual Part 4, Temporary Revisions 04-64 and 04-65, both dated March 30, 2024. The temporary revisions correct the necessary changes requested by the commenter. However, the inspection instructions are unchanged. It would not result in an unsafe condition if an operator were to follow a previous revision; therefore, no changes are necessary in this proposed AD.

Requests To Clarify Terminating Action

United requested that paragraph (i) of the proposed AD be amended to clarify that only a permanent repair will be considered a terminating action for the repetitive inspection on the repaired wing. United added that since there is no defined repair in the requirements bulletin at this time, the requirement of the repair note in note (a) of Boeing Alert Requirements Bulletin 777-57A0125 RB, dated July 25, 2023, and paragraph (i) of the proposed AD is unclear. United also requested clarification of the terminating action based on Boeing Alert Requirements Bulletin 777-57A0125 RB, dated July 25, 2023, which states that repair for any crack found on the (left or right) wing is terminating action to the repeat inspections “for the affected wing only,” compared to paragraph (i) of the proposed AD, which stated that a repair terminates the inspections “at the repaired location only.”

Air New Zealand (ANZ) requested greater clarification of paragraph (i) of the proposed AD. ANZ has inspected one airplane (applicable to Group 4 effectivity) and found a crack on the left wing. ANZ had a repair completed to a single fastener location, although six additional fasteners in the inspection area of the repair were also replaced at that time. ANZ noted that the repair instructions include inspection times that are different than those specified in the service information for fasteners that are inspected without a crack finding. ANZ believed the terminating action statement in the proposed AD referred to the repaired fastener only, and not the other fastener locations identified in the service information.

Etihad Airways requested that paragraphs (i) and (j) of the proposed AD be amended to state that only permanent repairs terminate the repetitive inspections required by paragraph (g) of the proposed AD. Etihad Airways noted that it had two airplanes with crack findings, which were temporarily repaired under FAA Form 8100-9 with statements that the repairs are Category C and must be replaced by a Category A or B repair within a certain time limit, and do not terminate the repeat inspection requirements of the service information.

The FAA partially agrees with the requests to amend paragraph (i) of the proposed AD for clarity. The affected area is the area covered by the repair. If a crack was found at one fastener location and the subject repair extends to additional fasteners, the affected repair area would include the initial cracked fastener location and the additional fasteners that are now within the repair. Follow-on repair inspections would affect the repair region. Areas outside of the repair would still be subject to the repetitive inspection requirements of paragraph (g) of this proposed AD. However, the FAA disagrees with the need to distinguish between temporary repairs and permanent repairs for terminating action because AMOC approvals are required for all temporary repairs and permanent repairs. Additionally, the FAA acknowledges that paragraph (i) that was in the proposed AD is not necessary, as Boeing Alert Requirements Bulletin 777-57A0125 RB, dated July 25, 2023, does not specify any standard repairs. Therefore, the FAA has removed paragraph (i) of the proposed AD and added an exception in paragraph (h)(3) of this proposed AD to clarify the requirements of the terminating action.

Request To Allow Certain Temporary Repairs as AMOCs

Etihad Airways requested that the proposed AD be revised to allow previously performed repairs approved under FAA Form 8100-9 that require continued inspections in the repaired area be approved as AMOCs to paragraph (g) of the proposed AD. The commenter noted that it had temporary repairs that do not terminate repeat inspections but are considered deviations to the inspection requirements.

The FAA agrees to clarify. AMOCs cannot be issued against proposed ADs. Any repairs, whether temporary or permanent, must be accomplished as specified in paragraph (h)(2) of this proposed AD. The provisions specified in paragraph (h)(3) of this proposed AD would then also apply to that repair.

Request for Change to Applicability

Boeing requested amending paragraph (c), “Applicability,” of the proposed AD to reflect the specific minor models of the 777 that are affected by the unsafe condition. Boeing noted that the proposed AD listed all of the Boeing Model 777 airplanes without aligning with the applicability of the requirements bulletin.

The FAA agrees with the request. Paragraph (c) of this proposed AD has been revised to reflect the requested change.

Requests for Alternative Part Number Options

United requested that alternative part number options be approved and communicated to operators to allow the inspections to be completed within the required time frame. United explained that certain parts within kits, required for inspection tasks for airplanes in groups 3 through 6, are not readily available from Boeing.

Air France reported that Boeing is unable to support the global need for parts, which would be a significant operational strain. Operators are obliged to work with very limited kits and support the high number of airplanes to be inspected. Air France suggested approval of a list of alternative parts that are readily available.

The FAA acknowledges the concerns regarding the parts not being readily available from Boeing. However, the FAA has not yet received an alternative part request from Boeing. The FAA will consider the approval of alternative parts or an extended compliance time in accordance with the procedures specified in paragraph (i) of this proposed AD, provided sufficient substantiation is provided to show an acceptable level of safety is maintained. The FAA has not changed this proposed AD as a result of these comments.

FAA's Determination

The FAA is proposing this AD after determining the unsafe condition described previously is likely to exist or develop in other products of the same type design. Certain changes described above expand the scope of the NPRM. As a result, it is necessary to reopen the comment period to provide additional opportunity for the public to comment on this SNPRM.

Material Incorporated by Reference Under 1 CFR Part 51

The FAA reviewed Boeing Alert Requirements Bulletin 777-57A0125 RB, dated July 25, 2023. This material specifies procedures for repetitive inspections for cracking of the upper wing skin common to certain fasteners and applicable on-condition actions. On-condition actions include repair.

This material is reasonably available because the interested parties have access to it through their normal course of business or by the means identified in the ADDRESSES section.

Proposed AD Requirements in This SNPRM

This proposed AD would require accomplishing the actions specified in the material already described, except as discussed under “Differences Between this Proposed AD and the Referenced Material,” and except for any differences identified as exceptions in the regulatory text of this proposed AD. For information on the procedures and compliance times, see this material at regulations.gov by searching for and locating Docket No. FAA-2023-2151.

Difference Between This Proposed AD and the Referenced Material

For certain conditions, Boeing Requirements Bulletin 777-57A0125 RB, dated July 25, 2023, specifies UT inspections. For the reasons explained under “Actions Since the NPRM was Issued,” this proposed AD would require open hole HFEC inspections instead of UT inspections for those conditions, as specified in paragraphs (h)(4) through (7) of this proposed AD.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would affect 323 airplanes of U.S. registry. The FAA estimates the following costs to comply with this proposed AD: